The present invention relates to novel and improved mechanical expansion anchors of the type used in anchoring an elongated bolt in a blind drill hole such as a mine roof. Such anchors include a radially expansible shell and a tapered plug, the present invention being directed particularly to improvements in the shell portion of the anchor, providing especially useful properties when the anchor is used in combination with a resin grouting material.
One of the most commonly employed means of supporting and reinforcing rock structures in underground mining and other excavating operations is the mechanical expansion anchor. Over the course of many years a wide variety of such anchors has been developed, all having in common some type of expansible shell structure and a tapered plug or nut which is placed on the threaded end of a bolt and moved axially on the threads by rotation of the bolt to cause radially outward expansion of the shell into tightly gripping engagement with the wall of a blind drill hole in the rock structure. More recently, mechanical expansion anchors have been installed concurrently with a resin grouting material which is typically supplied in a two-compartment package. The resin package or cartridge is inserted into the drill hole in advance of the end of the bolt carrying the expansion anchor and is ruptured to release and permit mixing of the resin components as it is forced against the blind end of the hole by advance of the bolt. As the bolt is rotated to expand the anchor, the resin components are mixed and subsequently harden to reinforce the anchorage.
One type of expansion anchor designed particularly for use in combination with a dual compartment resin cartridge is shown and described in U.S. Pat. No. 4,764,055, the disclosure of which is incorporated herein by reference. The present invention will be described in the context of an expansion anchor having the same structure as that of the referenced patent, with the addition of improved features of the present invention; it will be understood, however that the improvements need not be incorporated in anchors having all specific features of that shown in the patent. Although it is desirable that the resin components flow around as well as through the expansion shell, it has hitherto been necessary to make the shell substantially equal in diameter to the drill hole in order to provide frictional engagement of the shell with the drill hole wall.
It is a principal object of the present invention to provide a mechanical expansion anchor having novel and improved features which cooperate to ensure that the desired expansion occurs and that resin grouting material is properly distribued about the anchor, and the bolt upon which it is carried, within a blind drill hole.
A further object is to provide a resin-reinforced mine roof bolt anchor having a radially expansible shell with novel and improved structure for frictionally engaging the wall of a blind drill hole while providing an annular space between the major external surface of the shell and the drill hole wall for distribution of the resin.
Another object is to provide a radially expansible shell for use with a tapered camming plug in a mechanical expansion anchor having novel means incorporated in the shell for ensuring that the desired expansion occurs upon rotation of a bolt threadedly engaged with the plug.
Other objects will in part be obvious and will in part appear hereinafter.